1. Field of the Invention
The present invention relates to an optical device and a projecting device using the same.
2. Description of the Related Art
A front projector (projection device) which is one image display device often use a discharging lamp as a light source and a transmissive liquid crystal device or DMD (Digital Micromirror Device) as an image modulation element, and thus can be combined with devices and optical systems through various improvements. In addition, in recent years, projection type image display devices using reflective liquid crystal panels (reflective optical modulation elements) having higher resolution have been also put into practical use.
In the market of front projectors, brightness of displayed images is an important factor for gaining superiority. The improvement in the brightness of projected images is a current trend, but is not easily realized since a difficult problem such as the need for a heat measure in the front projector device exists.
For example, the increase in a temperature of the inside of the front projector device increases temperatures of constituent components. It is known that the linear expansion of the constituent component of which the temperature increases causes several defects. One of the defects is a registration shift. The registration shift is a phenomenon in which three image light beams of RGB do not overlap with each other at a correct position on a screen but are misaligned, and thus projected images look blurred.
In the front projector using the reflective liquid crystal panels, three images overlap with each other on the screen using a projection lens by allowing the image light beams obtained by three reflective liquid crystal panels to pass through a reflective polarizer or a color synthesis prism which synthesizes the image light beams. The positions of the reflective liquid crystal panels are regulated such that three images overlap with each other on the screen and are fixed using an adhesive or the like. However, the linear expansion in the constituent elements after being fixed shifts the position of each reflective liquid crystal panel and causes the registration shift.
Therefore, a projector has been proposed in which two fixing plates are joined to upper and lower edges of a light incidence surface of a color synthesis prism roughly parallel to each other, and the color synthesis prism, a reflective polarization element, and reflective liquid crystal panels are installed (for example, refer to Japanese Patent No. 4285462). According to the proposal, since the plate-shaped polarization element is fixed to the light incidence surface of the color synthesis prism via the fixing plate having a relative low linear expansion coefficient, it is possible to prevent the registration shift with a simple structure in the front projector.
In addition, there has been proposed a reflective projection display device which includes reflective liquid crystal panels, a wave plate provided in a reflective polarizer, a wave plate holder which holds the wave plate and has a first aperture, and a transmission window (a second aperture) which is provided between the wave plate holder and the reflective polarizer and is smaller than the first aperture (for example, refer to JP-A-2007-108735). According to the proposal, since unnecessary light does not reach the wave plate holder due to the second aperture smaller than the first aperture of the wave plate holder, a temperature of the wave plate does not increase, and for this reason, it is possible to prevent shading from being generated in images on the screen due to birefringence occurring in the wave plate.